A pole tube and an actuation magnet are described in the publication titled “Die Bibliothek der Technik” [Library of Technology], volume 118; authored by Klaus-Dieter Linsmeier, published by Verlag Moderne Industrie, 1995, incorporated by reference herein. According to this publication, a pole tube of an actuation magnet has a pole piece on the front face that is connected to a tube piece or yoke via a spacer ring made of non-magnetic material. An armature is movably mounted inside the pole tube and the final stroke position (operating stroke) of this armature is defined when it makes contact with a front face of the pole piece or with a non-stick platelet attached thereto. In the transition area between the spacer ring and the pole piece, a so-called control cone is formed that widens in the direction of the stroke. The geometry of this control cone is selected in such a way that the characteristic curve of the proportional magnet runs essentially linearly. Such electromagnets are employed, for example, to actuate the valve stems or pistons of hydraulic valves and, depending on the application case and on the way the valve is triggered, the interior of the pole tube can be charged with a very high pressure. The pole tube can fail owing to the high internal pressure and the resulting high mechanical loads, so that damage such as, for instance, crack formation, can occur, especially in the transition area from the spacer ring to the tube piece.